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Technical Report Documentation Page
1. Report No.
FHWA/ NC/ 2006- 48
2. Government Accession No.
3. Recipient’s Catalog No.
4. Title and Subtitle
Design Criteria for Post and Beam Bents with Drilled Shafts
5. Report Date
December 2007
6. Performing Organization Code
7. Author( s)
Brent Robinson, Aidcer Vidot, Young Jin Park, Ben Possiel, Vinicio Suarez,
Mervyn Kowalsky, and Mohammed Gabr
8. Performing Organization Report No.
9. Performing Organization Name and Address
Department of Civil Engineering
CB 7908, Mann Hall
North Carolina State University
Raleigh, NC 27695- 7908
10. Work Unit No. ( TRAIS)
11. Contract or Grant No.
2006- 15
12. Sponsoring Agency Name and Address
13. Type of Report and Period Covered
Final Report
North Carolina Department of Transportation
Raleigh, NC 27611
July 2005- June 2007
Federal Highway Administration
Raleigh, NC 27611
14. Sponsoring Agency Code
15. Supplementary Notes
16. Abstract
The research work presented in the report addresses the potential areas of conservatism in the current practice related to bridge
bents supported by drilled shafts and piles. The research encompasses modeling efforts and an experimental program. Modeling
includes analysis of existing bridge case studies with drilled shaft foundations to characterize the impact of the current
assumptions on sizing the various components of a bridge bent. An experimental program is performed to evaluate the
connection stiffness, and to determine if a given connection has sufficient capacity to develop such stiffness and transfer moment
The experimental program includes testing bearing pads in compression and shear to define their index properties. The bearing
pads are then tested in a prototype bridge set up to measure their performance under simulated loading.
An improved set of design guidelines and recommendations regarding the superstructure- substructure connection’s rotational
stiffness, shaft/ pile top boundary conditions, and resistance factors are proposed along with characterizing the impact of the
current practice and various design assumptions on sizing components of bridge bents. Resistance factors are developed for
drilled shafts, based on load test data from the state’s geologic regions, for compatibility with LRFD implementation. Work in
the report serves to provide a better understanding of the performance of bents supported by drilled shafts under AASHTO
loading conditions. Such understanding serves as a tool that provides NCDOT engineers with the flexibility of specifying the
level of conservatism to be built into a specific bridge bent design.
17. Key Words
Analysis, Database, Design, LRFD, North
Carolina, Drilled Shafts, Full Scale Testing,
Elastomeric Bearing Pads, Reliability, Resistance
Factors, Soil, Bridges
18. Distribution Statement
19. Security Classif. ( of this report)
Unclassified
20. Security Classif. ( of this page)
Unclassified
21. No. of Pages
199
22. Price
Form DOT F 1700.7 ( 8- 72) Reproduction of completed page authorized

Technical Report Documentation Page
1. Report No.
FHWA/ NC/ 2006- 48
2. Government Accession No.
3. Recipient’s Catalog No.
4. Title and Subtitle
Design Criteria for Post and Beam Bents with Drilled Shafts
5. Report Date
December 2007
6. Performing Organization Code
7. Author( s)
Brent Robinson, Aidcer Vidot, Young Jin Park, Ben Possiel, Vinicio Suarez,
Mervyn Kowalsky, and Mohammed Gabr
8. Performing Organization Report No.
9. Performing Organization Name and Address
Department of Civil Engineering
CB 7908, Mann Hall
North Carolina State University
Raleigh, NC 27695- 7908
10. Work Unit No. ( TRAIS)
11. Contract or Grant No.
2006- 15
12. Sponsoring Agency Name and Address
13. Type of Report and Period Covered
Final Report
North Carolina Department of Transportation
Raleigh, NC 27611
July 2005- June 2007
Federal Highway Administration
Raleigh, NC 27611
14. Sponsoring Agency Code
15. Supplementary Notes
16. Abstract
The research work presented in the report addresses the potential areas of conservatism in the current practice related to bridge
bents supported by drilled shafts and piles. The research encompasses modeling efforts and an experimental program. Modeling
includes analysis of existing bridge case studies with drilled shaft foundations to characterize the impact of the current
assumptions on sizing the various components of a bridge bent. An experimental program is performed to evaluate the
connection stiffness, and to determine if a given connection has sufficient capacity to develop such stiffness and transfer moment
The experimental program includes testing bearing pads in compression and shear to define their index properties. The bearing
pads are then tested in a prototype bridge set up to measure their performance under simulated loading.
An improved set of design guidelines and recommendations regarding the superstructure- substructure connection’s rotational
stiffness, shaft/ pile top boundary conditions, and resistance factors are proposed along with characterizing the impact of the
current practice and various design assumptions on sizing components of bridge bents. Resistance factors are developed for
drilled shafts, based on load test data from the state’s geologic regions, for compatibility with LRFD implementation. Work in
the report serves to provide a better understanding of the performance of bents supported by drilled shafts under AASHTO
loading conditions. Such understanding serves as a tool that provides NCDOT engineers with the flexibility of specifying the
level of conservatism to be built into a specific bridge bent design.
17. Key Words
Analysis, Database, Design, LRFD, North
Carolina, Drilled Shafts, Full Scale Testing,
Elastomeric Bearing Pads, Reliability, Resistance
Factors, Soil, Bridges
18. Distribution Statement
19. Security Classif. ( of this report)
Unclassified
20. Security Classif. ( of this page)
Unclassified
21. No. of Pages
199
22. Price
Form DOT F 1700.7 ( 8- 72) Reproduction of completed page authorized